Sperm selection in natural conception: what can we learn from Mother Nature to improve assisted reproduction outcomes?

Nicolas Garrido,Denny Sakkas,Christopher L.R. Barratt,Mythili Ramalingam

doi:10.1093/humupd/dmv042

Nicolas Garrido, Denny Sakkas

Open Access

https://doi.org/10.1093/humupd/dmv042

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Abstract

BACKGROUNDIn natural conception only a few sperm cells reach the ampulla or the site of fertilization. This population is a selected group of cells since only motile cells can pass through cervical mucus and gain initial entry into the female reproductive tract. In animals, some studies indicate that the sperm selected by the reproductive tract and recovered from the uterus and the oviducts have higher fertilization rates but this is not a universal finding. Some species show less discrimination in sperm selection and abnormal sperm do arrive at the oviduct. In contrast, assisted reproductive technologies (ART) utilize a more random sperm population. In this review we contrast the journey of the spermatozoon in vivo and in vitro and discuss this in the context of developing new sperm preparation and selection techniques for ART.METHODSA review of the literature examining characteristics of the spermatozoa selected in vivo is compared with recent developments in in vitro selection and preparation methods. Contrasts and similarities are presented.RESULTS AND CONCLUSIONSNew technologies are being developed to aid in the diagnosis, preparation and selection of spermatozoa in ART. To date progress has been frustrating and these methods have provided variable benefits in improving outcomes after ART. It is more likely that examining the mechanisms enforced by nature will provide valuable information in regard to sperm selection and preparation techniques in vitro. Identifying the properties of those spermatozoa which do reach the oviduct will also be important for the development of more effective tests of semen quality. In this review we examine the value of sperm selection to see how much guidance for ART can be gleaned from the natural selection processes in vivo.

Highlights

In 1992 a landmark study that recovered artificially inseminated spermatozoa from the Fallopian tubes of a woman undergoing total abdominal hysterectomy showed that of the hundreds of million sperm deposited in the female tract only a thousand or less are recovered from the Fallopian tubes (Williams et al, 1992)
In this review we examine the value of sperm selection to see how much guidance for assisted reproductive technologies (ART) can be gleaned from the natural selection processes in vivo
With the advent of assisted reproductive technologies (ART) and in particular intra cytoplasmic sperm injection (ICSI), the identification of characteristics encompassed by the ‘best’ male gamete are not always deemed important to search for and when preparing sperm the samples are fundamentally mistreated compared with the care we take with eggs

Summary

Introduction

In 1992 a landmark study that recovered artificially inseminated spermatozoa from the Fallopian tubes of a woman undergoing total abdominal hysterectomy showed that of the hundreds of million sperm deposited in the female tract only a thousand or less are recovered from the Fallopian tubes (Williams et al, 1992). In natural conception only a few sperm cells reach the ampulla or the site of fertilization Whether this population is a more fecund group of cells compared with other motile cells that are ejaculated, or those that successfully transverse the cervix is unknown (Williams et al, 1993). In this review we examine some of the in vivo selection processes to see whether they could be exploited for the improvement of laboratory tests of sperm quality and how they relate to current and future sperm selection strategies

Methods

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Conclusion